In the course of a lifetime, cancer will strike about one in three women and one in two men. More than 560,000 die from it each year in the United States alone. Early detection and treatment is currently the leading method to reduce cancer death, especially if the cancer is detected before metastasis. For nearly all types of cancer, the 5-year relative survival rate is substantially lower if the disease is caught at an advanced stage. Moreover, the financial costs of cancer treatment at an advanced stage can be an additional burden. By 2020, the cost of cancer treatment is expected to be $207 billion annually in the United States. Accordingly, early detection of cancer is important for increasing cancer survival rates and reducing the cost of treatment.
However, methods for early detection often lack sensitivity and generate numerous false positives and negatives. False negatives lead to missed opportunities to intervene early, and false positives lead to additional unnecessary testing, which can include biopsies and other painful, stressful and expensive procedures. The overall health burden borne by test subjects who register as false positives can outweigh the benefits to those patients who benefit from early detection of their cancers. This is especially true for screening tests where the incidence of disease is low. In addition, conventional screening tests, such as colonoscopies, are often invasive; hence, individuals are often resistant to undertake them. Thus, there is a need for a cancer diagnostic test that produces an unambiguous result, is low cost and minimally invasive, and has few false negatives and few false positives. Such a test would be useful for recurrence testing, validation or confirmatory testing, and other situations where an initial indication of cancer needs to be verified before an expensive and aggressive follow-up procedure is performed. When considering a confirmatory test, it is well known that up to 95% of biopsies return negative results (meaning the early indication of cancer was not verified by the painful, expensive procedure). Consequently, a simple, non-invasive, inexpensive test that could either confirm the need for a biopsy or eliminate the need for one, would be very valuable to patients and the healthcare system.
Currently, a type of diagnostic called Liquid Biopsy is being investigated as a technique for determining the presence of cancer in a test subject by analysis of a blood sample or other easily obtained bodily fluid. Many different characteristics of the blood sample are being investigated. These include analysis of deoxyribonucleic acid (DNA), ribonucleic acid (RNA), proteins, microRNA, exosomes, and other potential biomarkers of cancer. However, many of these liquid biopsy methodologies rely on expensive analytical techniques such as DNA or RNA sequencing.
These tests often require extensive levels of multiplexing that make them expensive, difficult to operate, and also difficult to interpret. Myeloid-Derived Suppressor Cells (MDSCs) are a type of cell known to be highly correlated with the presence of malignant solid tumors, and they are present at low levels in the blood. Studies have shown that MDSCs are concentrated in the tumor environment and function to suppress immune response to the tumor. Their presence in peripheral circulation is believed to be due to spilling of these immature cells from the tumor into the vasculature. Extensive work has shown that shifts in the MDSC population that are correlated with cancer can be detected using Flow Cytometry, an inexpensive, widely used, and reliable method of cellular population analysis. However, conventional methods of flow cytometry data analysis as applied to MDSCs in blood samples are not sufficiently accurate to allow MDSCs to be used as a sole biomarker for a cancer detection screening test for the general public. Flow cytometers can process a sample containing hundreds of thousands of cells, or more, suspended in a fluid medium and provide detailed distinguishing information on each individual cell in the sample. The conventional method of analysis of flow cytometry data relies on a technique called gating. Gating is a method of sequentially applying threshold cutoffs to one- or two-dimensional projections of the multidimensional data set in order to isolate a specific population or populations and count the number of cells in the isolated populations. While this method is suitable for research studies and some diagnostic applications, for cancer detection, this method of analysis can be labor intensive, subjective, and results in a very coarse representation of the flow cytometer output data, often obscuring or ignoring a great deal of information available regarding the relative distributions of all the cell populations and the shape of the distributions of the isolated cell populations. Thus, a flow cytometer analysis method that can be utilized to identify target cells indicative of cancer reliably, economically, and with the required specificity and sensitivity is needed.